Its harrowing to be a passenger. I drive myself everywhere now.
I think a better design than an audible alarm is to show the driver using quadrants or a diagram when an object is within the "close," "very close," or "near-collision" zone around a vehicle and beep once but only when the object passes into another zone to alert the driver to a change in state. The tones should change for each transition so you can learn the tone for "object moved from close to very close in right driver's-side zone" and distinguish that from "object moved from very close to close in right driver's-side zone."
Having to constantly pay attention to an alarm tone is extremely nerve-wracking. In medical devices this will often result in "alarm fatigue" where you spend so much time dealing with false alarms that you miss a real alarm.